Art of mounting piezoelectric crystals



' Jan. 14, 1941.. H. w. N. HAWK ART OF MOUNTING PIEZOELECTRIC dYRSTALS Filed May 31, 1939 (Ittorneg Patented Jan. 14, 1941 UNITED STATES ART OF MOUNTING PIEZOELECTRIC CRYSTALS Henry W. N. Hawk, Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application May 31, 1939, Serial No. 276,677

7 Claims.

This invention relates to the art of mounting piezoelectric crystals.

The principal object of the invention is to provide an extremely compact and trouble-free mounting for piezoelectric crystals.

Another and important object of the invention is to provide a simple, inexpensive, hermeticallysealed, piezoelectric apparatus and one which, by reason of its ease of assembly and economy of parts, lends itself readily to mass production methods.

Other objects and advantages, together with certain details of construction, will be apparent and the invention itself will be best understood by reference to the following specification and to the accompanying drawing, wherein Figure 1 is a side elevational view of at hermetically-sealed holder containing a piezoelectric crystal mounted in accordance with the principle of the invention;

Figure 2 is a sectional view taken on the line 2-2 of Fig. 1; and

Figure 3 is an exploded view of the device of Figs. 1 and 2.

In the drawing, wherein like reference characters designate the same or corresponding parts in all figures, I designates a quartz or other crystal having piezoelectric properties. Contiguous the opposite electrode faces of the crystal are electrodes 2 and 4, respectively, which preferably comprise adherent or integral coatings of evaporated metal but which may be in the form of removable metal plates.

As more clearly shown in Fig. 3, the electrodes 2 and 4 are arranged in staggered relation on the opposite electrode faces of the crystal, that is to say, each electrode covers less than the entire area of an electrode face so that there is an exposed marginal area ct adjacent the edge of the top face of the crystal and another marginal area b adjacent the diametrically opposite edge of its bottom face. In cases where it is desirable to fix the capacitance between the electrodes at a certain value, the opposite overlapping portions of the electrode may be of an area calculated to provide such certain value of capacitance.

A separate mounting or clamping force is applied to the crystal adjacent its exposed areas a and b through the separate electrodes 2 and 4 as by means of conductive clamps 3 and 5, respectively. The jaws of these clamps may be of any suitable design but in no event should either of them come in contact with both of the electrodes; otherwise short circuiting would occur. The clamps are provided each with conductive extensions comprising a wire or a ribbon-like electrodelead 3w and 510, respectively, through which the crystal is energized.

The crystal and its electrode assembly are preferably enclosed, in accordance with the invention, in a small hermetically-sealed molded insulating casing 6 through whiclt the oppositely located electrode leads 3w and 5w extend. This casing 6 is preferably constituted of styrol or a polymerization product thereof, or of other moistureproof thermo-plastic or thermo-setting material 0 possessing the requisite electrical and mechanicalresistive properties.

As indicated in Fig. the casing may be made in two sections 60 and Ed of duplicate size and contour. Each of the sections is provided with a central recess 1 and a pair of slots 8, 9, respectively, which extend in opposite direction from the recess and communicate with the exterior of the section. The dimensions of the recess 1, when the casing sections 60 and 6d are joined, is somewhat greater than is required to accommodate the crystal and its electrode, so that the entire assembly may be supported out of contact with the walls of the recess. The dimensions of the slots 8 and 9 are such as to afford a snug fit for the electrode leads 3w and 5w, respectively. In order to insure accuracy in the spacing of the clamps 3 and 5, the leads 3w and 5112 may each be provided with one or more right-angle bends, x, which abut against the side walls of the casing. For a casing of given dimensions, the spacing of these bends depends upon the size of the particular crystal to be accommodated within that casing.

The preferred manner of assembling the several parts is as follows: The electrode leads 3w, 5w are both pressed or otherwise fitted! into the slots 8, 9, respectively, in the same casing section, say section 60. Prior to fitting the leads into their slots, that part of each lead which is to be accommodated within a slot may be coated with a styrol or other suitable cement. When the clamps 3 and 5 on the respective inner ends of leads 3w. 510 are of the type shown in the drawing, the open side ends a of both clamps should be presented to the open end of the recess. With the clamps in the described position, the crystal I and its electrodes 2 and 3 are urged into the open sides thereof so that one jaw of each clamp contacts an electrode and the other jaw contacts an ex- 5 posed marginal edge of the crystal. The other section, 6d, of the casing is then fitted over the first mentioned casing 60, the alignment of the casing sections being ensured when the sections between the bends a: and y of the electrode leads fit within the slots 8 and 9 of both of the casing sections 60, 6d. Cement may be applied between the abutting surfaces of the casing sections to form a seal or, if the casings are made of a thermoplastic (as distinguished from a thermo-setting) material, a hot iron may be run around the seam to weld the casing sections together.

Other modifications of the invention will suggest themselves to those skilled in the art. It is to be understood therefore that the foregoing is to be interpreted as illustrative and not in a limiting sense except as required by the prior art and by the spirit of the appended claims.

What is claimed is:

1. In combination, a piezoelectric crystal, a pair of electrodes each partially covering an electrode face of said crystal, the uncovered area of each of said crystal faces being in register, respectively, with a covered area of the other of said crystal faces.

2. The invention as set forth in claim 1 and wherein said electrodes are integral with the electrode faces of said crystal.

3. In combination, a piezoelectric crystal, a pair of electrodes each partially covering an electrode face of said crystal, said electrode faces having non-covered areas adjacent opposite edge portions of said crystal, and a pair of supporting members secured to said crystal adjacent the said noncovered areas of its said electrode faces, each of said supports contacting one of said electrodes and comprising an electrical connection thereto.

4. In combination, a piezoelectric crystal, a pair of electrodes secured respectively to the opposite electrode faces of said crystal, said electrode faces having non-covered areas adjacent diagonally opposite edge portions of said crystal, and means for supporting said crystal at its said diagonally 0pposite non-covered areas.

5. In combination, a piezoelectric crystal, a pair of evaporated-metal electrodes partially covering the electrode faces of said crystal, the non-covered areas of said electrode faces being adjacent opposite ends of said crystal, and a pair of supporting members secured to said crystal adjacent the said non-covered areas of its electrode faces, each of said supports contacting one of said electrodes and comprising an electrical connection thereto.

6. In combination, a piezoelectric crystal having opposite faces each partly covered with a metal film, the metal covered areas of said crystal faces comprising electrode areas, the non-covered areas of said faces being at opposite ends of said crystal, and a clamp adjacent each of the said crystal ends, each clamp contacting the non-covered area of one face and the metal covered area of the other face.

'7. A device of the character described comprising a molded casing, a hermetically sealed compartment therein, said compartment containing a piezoelectric crystal having opposite major faces each partly covered with a metal film, the metal covered areas of said major faces comprising electrode areas, the non-covered areas of said major faces being at opposite ends of said crystal, a clamp adjacent each of the said crystal ends, each clamp contacting one metal covered area of one face and the non-covered area of the other face, and an electrode lead connected to each clamp, said leads extending in opposite directions to the exterior of said molded casing.

HENRY W. N. HAWK. 

